While there is a large body of information available on the types of reactions and substrates that are amenable to antibody catalysis, we are only beginning to understand the structural features of antibodies that lead to catalysis. The purpose of this proposal is to carry out detailed studies of a number of novel antibody-catalyzed reactions, including a ferrochelatase that catalyzes metal ion insertion into porphyrins, and two efficient acyl group transfer catalysts that function by different mechanisms. We are undertaking an extensive effort to characterize these antibodies using x-ray crystallography, kinetic studies and mechanistic studies. We are also exploiting these antibodies as model systems to explore the evolution of binding and catalytic function both in vivo and in vitro. The immunological evolution of antibodies through the affinity maturation of their germline precursors is being characterized by detailed biophysical, kinetic and structural studies. In addition, a number of general strategies are being explored to evolve enhanced catalytic function in vitro, including cofactor and phage-based selections. These studies should provide important insights into the evolution of binding energy and catalytic function in nature, and should also provide important new approaches for generating antibodies with improved catalytic properties.